The present invention is generally related to compositions, methods and apparatus for producing gaseous mixtures. In particular, the present invention is related to methods for rapidly producing gaseous mixtures that are particularly useful for mitigating major disruption events in plasmas such as those created in magnetically confined fusion plasma devices.
Gaseous plasmas generally consist of mixtures of electrons, positively charged ionic species, and neutral gaseous atoms and/or molecules. In various devices, magnetic fields are used, to confine the hot plasma within a containment vessel so that the plasma does not touch the vessel wall.
The phenomenon known as major disruption of a magnetically confined plasma is a fast and detrimental process by which the large amount of thermal and magnetic energy, that normally exists in a magnetically confined plasma is transferred to the wall of the plasma containment vessel, leading to its damage, up to and including melting and vaporization of the wall material. Such disruptions are created by macroscopic instabilities in the plasma that cause a rapid thermal quench of the plasma column. The disruption phenomenon also produces large forces acting on the mechanical structure of the containment vessel. Magnetically confined plasma devices such as the International Thermonuclear Experimental Reactor (ITER) now under construction would benefit from a reliable and real-time process for preventing or mitigating this phenomenon.
The basic approach to plasma disruption mitigation involves quickly converting the thermal and magnetic energy of the plasma, which is typically characterized by a plasma energy density of approximately 1 gigajoule (GJ) in a volume of approximately 1,000 cubic meters in a device such as the ITER, into radiation within a time period of approximately 1 millisecond, while simultaneously increasing the density of free and bound electrons in the plasma by a factor of approximately 100 over the entire plasma cross section. This process suppresses the conversion of the plasma and magnetic field energy into an avalanche of high energy runaway electrons, which would otherwise reach the wall of the plasma containment vessel and cause its melting and vaporization.
One specific version of this approach is known as the impurity injection method.. One impurity injection method involves ionizing an impurity gas to form an impurity plasma, followed by electro-dynamic acceleration of the impurity plasma and its injection into the target plasma, which converts the target plasma energy into radiation and provides a harmless and rapid quench of the plasma thermal energy and current.
This method must utilize enough mass of an impurity gas of sufficiently high atomic number, which must be injected with a density and velocity that are sufficiently high that the impurity ions penetrate to the core of the hot plasma and strongly radiate the energy on the fast disruption time scale in order to achieve real-time mitigation. High pressure jets of neutral gaseous species, such as the inert gases neon or argon, have been considered for this purpose in the technique known as massive injection. However, one well recognized problem is that once the impurity gas atoms are ionized in a thin outer layer of the hot plasma, they can no longer penetrate the confining magnetic field unless they possess a sufficiently high velocity to overcome the magnetic pressure of the magnetic field confining the plasma. The injection velocity of a neutral gas is limited to a relatively low value and thus the mitigation process must rely on the inward propagation of a cooling front wave, enhancement of magneto-hydrodynamic (MHD) activity, and mixing of impurity gas into the core plasma. These processes take a relatively long time time, estimated to be at least 40 milliseconds for the ITER device. Moreover, controlling the sequence and timing of these processes is difficult, yet they are necessary to obtain reliable and prompt disruption mitigation.
One approach to the problem of delivering an impurity gas having sufficient mass to penetrate a plasma has been the proposed use of “dusty” plasma, which is an ionized gas containing particles of carbon, or other particulate material, having a size on the order of 10 microns in diameter. One problem with such an approach, however, is that the injection plasma must be accelerated, and the particulate matter in such a plasma is very heavy, such that it must be dragged b the ambient accelerated plasma, a process that limits the velocities that can be obtained with the particulate material.
Accordingly, it is the object and purpose of the present invention to provide a composition that is capable of rapidly producing on demand a gas that is suitable for mitigating disruptions in plasmas, as well as methods for making such a composition and producing the gas from such composition on demand.